A traditional motorcycle comprises a handle control (conventionally the grip on the right of the handlebar), which is rotationally mounted and mechanically connected to an engine control which adjusts the generation of the driving torque. Normally, the handle control is connected to the engine control by means of at least one Bowden-type metal cable, which is inserted into an external sheath to slide with respect to the sheath and is biased by a spring towards a rest position corresponding to a zero driving torque.
Recently, deriving from the experience accrued in the automotive industry, the application of DBW (Drive By Wire) systems has been suggested, in which the handle control is no longer mechanically connected to the engine control, but is connected to a position sensor only, which detects the position of the handle control, and therefore drives an actuator which mechanically operates the engine control.
The greatest issue that needs to be addressed in designing a DBW system suitable for being used on a motorcycle is the implementation of an acquisition system for detecting the angular position of the handle control. Indeed, such an acquisition system must be able to provide a rapid and errorless interpretation of the driver's intention of accelerating/decelerating, must provide information redundancy so as to ensure certain interpretation of the driver's intention by an engine control unit, and must be installable in the context of a motorcycle taking into account the issues related to the volumes, the high vibrations which may occur on a motorcycle, and to the adverse environmental conditions related to the lack of protection (accidental shocks, very low or very high temperature, water splashes, etc.).
Furthermore, an acquisition system suitable for being used in a motorcycle must be highly versatile in order to be easily integrated even on very different motorcycles, because the production of motorcycles is highly fragmented and characterized by a vast production of models often in small numbers.
In the automotive field, there are various solutions for implementing an acquisition system for detecting the position of the gas pedal; however, such automotive solutions may not be used on a motorcycle as they are too cumbersome and not rugged enough. Furthermore, in motorcycle applications, the safety and rapidity of interpreting the driver's intention is even more important than in automotive applications, because a car resting on four wheels is intrinsically stable, and thus a short discrepancy between the delivered driving torque and the driver's intention is tolerable (i.e. is essentially not dangerous) when driving a car; instead, a motorcycle resting on two wheels only is intrinsically unstable and is based on a dynamic balance which may be easily upset, even by a short discrepancy between the delivered driving torque and the driver's intention (particularly under limit conditions, such as while cornering).
Patent application US20080154537A1 suggested an acquisition system for detecting the angular position of a motorcycle handle control; the acquisition system is provided with: a fixed supporting body; a movable element, which is movably mounted in the supporting body; a transmission device mechanically connected to the handle control and to the movable element to transmit the motion of the handle control to the movable element; a main position sensor, which is carried by the supporting body, is coupled to the movable element to determine the angular position of the movable element, and is adapted to provide two reciprocally redundant measurements of the angular position of the movable element; and a control position sensor, which is different and independent from the main position sensor, is carried by the supporting body, is coupled to the movable element to determine the position of the movable element, and is adapted to provide two reciprocally redundant measurements of the position of the movable element.
The acquisition system described in patent application US20080154537A1 is very rugged and reliable, but on the other hand has relatively high volumes and requires a mechanical connection by means of Bowden cables between the handle control and the movable element mounted in the fixed supporting body.
U.S. Pat. No. 6,832,511B2 describes an angular position sensor for detecting the angular position of a motorcycle handle control; the position sensor is installed by the side of the handle control and comprises a double potentiometer, which provides two reciprocally redundant measurements of the position of the movable element and is provided with a rotating shaft which is made angularly integral with the handle control by means of a mechanical transmission device.
The angular position sensor described in patent U.S. Pat. No. 6,832,511B2 has the drawback of being not very reliable, because the use of a potentiometer arranged at one end of the handlebar is very problematic due to the high vibrations present in this area; in other words, a potentiometer provides for a sliding contact between one or more movable sliders and a fixed plate, and such a sliding contact is very sensitive to mechanical vibrations. During the normal run of a motorcycle, the ends of the handlebar are subjected to very high vibrations due to the amplifying effect of the handlebar (i.e. a vibration transmitted to the handlebar at a central area of fastening the handlebar to the front fork is multiplied by the arms of the handlebar and is thus greatly amplified at the ends of the handlebar). Such vibrations may negatively affect the reading provided by the potentiometer, because they may cause undesired, uncontrolled oscillations on the position of the potentiometer sliders, which cause a high degree of uncertainty on the measurement provided by the potentiometer; furthermore, over time, such vibrations may deteriorate the potentiometer thus determining early, unpredictable wear with negative potential impacts on the driver's safety.
Patent application WO2008010186A2 discloses a twist-grip control device for motor vehicles comprising: a stator portion which is stationary in operation, a rotor portion which may be gripped and which is mounted such that it can be manually rotated about an axis with respect to the stator portion, against the action of an opposing spring, a first and a second permanent magnet connected to the rotor portion in respective separate angular fields about said axis and adapted to generate respective predetermined angular distributions of magnetic field intensity about said axis, first and second magnetic field sensors connected to the stator portion in respective separate angular positions about said axis, and associated with the first and second permanent magnets respectively in order to provide, when the rotor portion; is rotated by a certain angle with respect to the stator portion, respective first and second electrical signals indicative of the relative angular position of the rotor portion. These signals are correlated with one another in a predetermined relationship such that one of the signals may be used as a control signal indicative of the extent of an associated controlled physical magnitude desired by the user, and the other signal may be used as a control signal adapted to enable the detection of the occurrence of operating malfunctions or failures when these signals are no longer correlated with one another in the predetermined relationship.
The position sensors used in the handle control device of patent application WO2008010186A2 require the use of permanent magnets for determining the angular position of the handle; however, using permanent magnets is relatively unsafe, because the magnetic field generated by these permanent magnets may be affected in an undesired, unexpected manner by surrounding metal objects (e.g. metal rings carried by the driver's right hand or metal reinforcements inserted in a glove worn on the driver's right hand) with a consequent deterioration of accuracy and speed in reading the angular position of the handle.